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Harp, Edwin L. , and Jibson, Randall W. , 1995, Inventory of landslides triggered by the 1994 Northridge, California earthquake: U.S. Geological Survey Open-File Report 95-213.Online Links:
This is a vector data set.
The map projection used is Transverse Mercator.
Planar coordinates are encoded using coordinate pair
Planar coordinates are specified in meters
The horizontal datum used is North American Datum of 1927.
The ellipsoid used is Clarke 1866.
The semi-major axis of the ellipsoid used is 6378206.4.
The flattening of the ellipsoid used is 1/294.98.
Value | Definition |
---|---|
0 | Corresponds to polygons in which landslides are not found, such as inliers |
1 | Corresponds to label points within landslide polygons |
David Keefer and Ray Wilson of the U.S. Geological Survey assisted in the post-earthquake reconnaissance efforts and in defining the landslide limits. John Michael and Art Tarr of the U.S. Geological Survey helped construct the digital landslide map. Al Barrows and Pam Irvine of the California Division of Mines and Geology, and Robert Larson of Los Angeles County provided useful information on the location and nature of many landslides triggered by the earthquake.
303-273-8557 (voice)
harp@usgs.gov
This extensive database will allow quantitative modeling of the relation between strong ground shaking, landslide susceptibility, and landslide distribution. The area of the greatest landslide concentration currently is undeveloped, but many parts of this area in the Santa Susana Mountains are slated for future dense residential development. We anticipate using the data and modeling results from the Northridge earthquake to produce regional maps of earthquake-induced landslide hazards that can be used to make informed decisions regarding development in the areas most susceptible to seismically triggered landsliding.
We estimate that location accuracy of landslides mapped from the airphotos to the paper base maps is generally within 10 m and no worse than 20 m. When the paper maps were registered on the digitizer, the computer calculated the root-mean-square (RMS) error in the base-map registration, which averaged 3.6 m and ranged from 0.2 to 10.4 m. Thus, landslide locations plotted on plates 1 and 2 are generally accurate within about 15 m and are no more than 30 m mislocated.
Landslides as small as 1-2 m across are visible where the slopes were sunlit;where slopes were partly shaded, slides about 5-10 m across are the smallest that could be resolved; thus, the inventory is not complete. However, our field observations indicate that south-facing slopes in most of the landslide area generally are steeper and produced far more landslides than north-facing slopes. Therefore, landslides on north-facing slopes that are not visible on the photos because of shadows probably account for only a small proportion of the total landslides. From our field investigations we estimate that we missed no more than about 20 percent of the landslides that exceeded 5 m in maximum dimension and no more than 50 percent of those smaller than 5 m. In terms of area, however, we estimate that we have mapped more than 90 percent of the area covered by triggered landslides, because most of the landslides that are not visible on the photos are small.
The Northridge earthquake provided an unprecedented amount of data for
studying the distribution and effects of landslides triggered by an
earthquake in an urban area. Detailed field investigations to document
earthquake-triggered landslides, which were initiated the day of the
earthquake, are continuing. In the first several days following the
earthquake, we drove outward from the epicentral area in all
directions to locate areas of concentrated landsliding and to find the
farthest extent of landsliding, which is defined by small rock and
soil falls from very susceptible slopes such as steep road and stream
cuts.
High-altitude aerial photography (nominal scale 1:60,000) of the
epicentral region was flown by the U.S. Air Force within hours of the
earthquake, and we mapped fresh landslides visible on these photos to
provide a detailed inventory of ground failures triggered by the
earthquake. We mapped more than 11,000 individual landslides on
1:24,000-scale U.S.G.S. topographic base maps. The photos show all but
the smallest slope failures and some that were hidden within deep
shadows on the north sides of steep slopes.
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US Geological Survey Open File Report 95-0213
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Data format: | Landslide map in format ARC/INFO export format (version 7.x) Size: 3.0 megabytes |
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Network links: |
<http://pubs.usgs.gov/of/1995/ofr-95-0213/downloads/landslide.e00.Z> |
703-648-6533 (voice)
703-648-6252 (FAX)
pschweitzer@usgs.gov